WASHINGTON—America's top diplomat says the U.S. relationship with Pakistan "could not be more important" as the Islamic republic grapples with economic and security woes and regional stability.

Secretary of State John Kerry spoke Sunday as he sat down with Pakistan Prime Minister Nawaz Sharif, who is in Washington this week for talks with the White House.

Kerry declined to answer questions after brief remarks to reporters at the State Department. But U.S. officials say the Obama administration is posed to release more than $1.6 billion in military and economic aid to help bolster ties with Islamabad that have deteriorated over deadly American airstrikes and the 2011 raid that killed Osama bin Laden in Pakistan.

"We have a lot to talk about, and the relationship with Pakistan could not be more important," Kerry said as his meeting with Sharif began. "On its own, (Pakistan is) a democracy that is working hard to gets its economy moving and deal with insurgency, and also important to the regional stability."

Sharif did not speak during the brief session with reporters.

The two men met over dinner, shortly before Kerry planned to head to Europe for peace talks for Syria and between Israel and Palestinian authorities.

He will be meeting with foreign ministers in Paris, London and Rome before returning to Washington on Thursday.